Aromatic hydrocarbons in fuels such as gasoline or diesel oil represent a source of atmospheric pollution. The aromatic content of middle distillates may be as high as 85 vol %. An illustrative light straight run gas oil may for example be typically found to contain about 30 vol % aromatics. As environmental considerations become of greater concern, it is desirable to treat hydrocarbons such as naphthas and middle distillate hydrocarbons to decrease the content of undesirable aromatic components. Noble metal catalysts, which are excellent for aromatics saturation will quickly get poisoned by the sulfur and nitrogen compounds that are present in typical hydrocarbon feedstocks, and lose their hydrogenation activity in a short time. Therefore, noble metal catalysts can not be used for a one-step process for hydrodearomatizing these fuel feedstocks. Since the prior art hydroprocessing catalysts, typified by sulfided, alumina supported cobalt/nickel/molybdenum/tungsten, sometimes promoted by phosphorus or fluorine, do not have the catalytic activities necessary for producing a product having a very low aromatic content, it is desirable to find a hydrotreating catalyst with very high aromatics saturation activity.
U.S. Pat. No. 1,965,956 is directed to the hydrogenation of aromatic compounds to hydroaromatic compounds with a gas consisting substantially of hydrogen under a pressure of at least 100 atmospheres, at a temperature between 200.degree. C. and 350.degree. C., in the presence of a "mixed catalyst" comprising metal compounds of group 1, group 6 and group 8 of the periodic system, on a wide variety of catalyst supports including active charcoal. The catalysts of U.S. Pat. No. 1,965,956 can also contain "activating admixture" selected from compounds of elements of groups 2 to 5 and of group 7 of the periodic system.
U.S. Pat. No. 2,608,521 is specifically directed to an improved process for the desulfurization of "sulfur bearing" hydrocarbon oils using "sulfactive hydrogenation catalysts". The "sulfactive hydrogenation catalysts" of U.S. Pat. No. 2,608,521 can consist of "oxides or sulfides of the transition metals", with or without such stabilizers and promoters as the oxides and carbonates of a very large selection of metals, in combination with a large selection of various conventional supporting materials.
U.S. Pat. No. 3,367,862 is directed to desulfurization of heavy residual hydrocarbons by hydrolysis with water in the presence of catalyst on a charcoal base.
U.S. Pat. No. 3,546,103 is directed to the removal of metals and coke from hydrocarbon resids by use of, as pre-catalyst, metals of Group IIB or Group VIB plus Group VIII, on charcoal.
U.S. Pat. No. 3,725,303 is directed to treating of aqueous solutions of oxy-sulfur compounds (such as sodium thiosulfate) by use of a catalyst containing molybdenum sulfide and cobalt sulfide on a carbon support.
U.S. Pat. No. 3,812,028 is directed specifically to "hydrotreating" fossil fuels containing polynuclear aromatic such as asphaltenes, and for converting the components boiling above 1000.degree. F. to products boiling below 1,000.degree. F. (this is actually hydrocracking), by the use of Group VI and/or Group VIII metals on carbon, at a hydrogen partial pressure in excess of 2,200 psig and at a temperature between 750.degree. F. and 850.degree. F.
U.S. Pat. No. 3,997,473 (and its divisional U.S. Pat. No. 4,032,435) is directed to hydrodesulfurization of petroleum residues by use of a catalyst comprising cobalt/nickel/molybdenum/tungsten on a carbon support, the carbon support being characterized by an average pore radius of at least 25 Angstroms and a BET Surface area of 200-800 m.sup.2 /g. The catalyst of these patents has a loading of Group VIB metal "of at least 10 and up to about 20 weight percent expressed as metal oxide based on the weight of the catalyst support."
U.S. Pat. No. 4,082,652 is directed to treatment of heavy oils, to effect hydrodesulfurization by use of a molybdenum/nickel or molybdenum/cobalt on carbon catalyst. The catalyst preparation requires that the molybdenum be deposited first, then sulfided, and only then that the nickel or cobalt be added.
U.S. Pat. No. 4,176,051 is directed to a process for catalytically hydrocracking a heavy hydrocarbon oil, wherein the heavy hydrocarbon oil is slurried with a particulate catalyst mass comprising aluminum compound coated coal and/or coke particles which may also be coated with a cobalt and/or a molybdenum compound, and then reacted with hydrogen.
U.S. Pat. No. 4,313,852 is directed to hydrotreating, particularly of coal liquids, in the presence of a sulfided molybdenum or tungsten on active carbon, with or without a second metallic component, in which catalysts the metal sulfides are substantially completely on the outer surface of the active carbon support. The carbon supported catalyst preparation according to U.S. Pat. No. 4,313,852 must involve direct deposition of metal sulfides on the carbon support and subsequent reduction to lower valent sulfides.
U.S. Pat. No. 4,831,003 is directed to a catalyst composition, useful in hydrotreating processes, prepared by depositing a compound of a metal of Group IIB, IVB, IVA, VA, VIA, VIIA, or VIIIA onto a carbon support formed simultaneously with the deposition, by partial combustion of an unsaturated hydrocarbon. The deposited metal is thereafter converted to an oxide or sulfide.
U.S. Pat. No. 5,051,389 is directed to a method for preparing a catalyst composition for hydroconversion processes wherein the catalyst composition is formed by depositing one or more metal and/or metal compounds from vapor phase, at elevated temperatures, onto a preformed carbon support which has maximum dimension in any direction of about 50 Angstroms to about 5,000 Angstroms. The catalysts made according to U.S. Pat. No. 5,051,389 have to be added to or combined with the carbonaceous material to be hydrotreated in only 50 to 5,000 parts per million concentration, for the hydroconversion process to take place (one-pass application).
There is a continuing need in the art for catalysts which demonstrate improved hydrodearomatization of middle distillate hydrocarbons. It would be extremely valuable if a catalyst which performed better with respect to dearomatization were capable of simultaneously eliminating sulfur and nitrogen.